1. Field of the Invention
The present invention relates to a technology for simulating a tactile sensation that a person would get when touching an object, and more particularly relates to a technology for simulating a tactile sensation to be gotten by him or her about the material or shape of that object.
2. Description of the Related Art
Recently, thanks to development of audiovisual technologies and network technologies and expansion of their infrastructures, video (visual information) and audio (audio information) can now be transmitted to any distant location with a rather high degree of reality. But there should be ever-increasing demands in the near future for transmitting such audiovisual information over telecommunications lines with even higher degree of reality and presence. To realize that, demands for not just further development of audiovisual technologies but also development of new technologies for communicating or simulating non-audiovisual information (i.e., information concerning the sense of touch or sense of smell) should rise in the future. Among other things, the tactile sensation is a feel that a person who has touched an object gets, and therefore, is a very ordinary sensation familiar to everybody, and would be said to be a very important sensation in order to give a high degree of presence to a recipient.
When a person touches an object, he or she receives various kinds of sensations, which can be classified into several categories including temperature-related sensations such as hot feel and cold feel, force-related sensations that he or she gets as pressure or stress when feeling the hardness or shape of the object, and tactile sensations such as soft feel or rough feel that he or she gets when feeling the material or shape at the surface of the object. It is known that among these various sensations, the force-related sensations and the tactile sensations are received through four mechanoreceptors called “Meissner corpuscles”, “Merkel's cells”, “corpuscles of Pacini” and “Ruffini ending” that are present under the human skin (see Iwamura, “Touch”, Igaku-Shoin Ltd., pp. 26-28 and pp. 208-211, (2001)). It has also turned out, as a result of recent researches, that these mechanoreceptors sense the pressure or vibration, which has been produced by a contact between the skin and the object, as a variation in strain energy density distribution (see Srinivasan, M. A. and Dandekar K., “An Investigation of the Mechanics of Tactile Sense Using Two-Dimensional Models of the Primate Fingertip”, Trans. ASME, J. Biomech. Eng., 118, (1996), pp. 48-55, and also see Kobayashi and Maeno, “Relationship between the Structure of Finger Tissue and the Location of Tactile Receptors: 2nd Report, Method of Dynamic Contact Analysis and Results for Contact between the Finger and Plane Plate”, Transactions of the Japan Society of Mechanical Engineers, Series C, (1998), pp. 4798-4805). In view of these considerations, a lot of researchers have already reported that if those mechanoreceptors are stimulated by giving some mechanical stimulation such as pressure or vibration to a person's skin surface using an actuator as a tactile simulator, then the person could get a tactile sensation that is quite different from the material feel of the tactile simulator itself.
For example, by paying special attention to the fact that when a person touches an object with unevenness, reactive force will be applied to the surface of his or her finger pulp perpendicularly to (i.e., along a normal to) that unevenness of the object, Japanese Patent Application Laid-Open Publication No. 2000-47567 discloses, in particular, on pp. 8-9 and FIGS. 8 and 9, a method for making the person virtually feel the surface unevenness of the object by controlling the direction of the reactive force to display. Specifically, for that purpose, in accordance with the information about the object's surface unevenness to simulate, normal vectors are defined in advance at respective very small intervals and reactive forces represented by those normal vectors are generated by a force transducer, thereby simulating the sensation to be gotten by feeling the uneven surface. Thus, it can be said that when some force is going to be simulated by displaying a reactive force, for example, a force-related sensation that a person gets when feeling mainly the hardness or shape of the object is going to be simulated.
Meanwhile, when a person attempts to get a material feel of the object by touching it, he or she “rubs” the object with his or her fingers. This movement is done probably because the person tries to get a tactile sensation of the object by making the mechanoreceptors under the finger skin sense the frictional vibration that has been produced by that “rubbing” movement. That is why in order to simulate a tactile sensation, it is an effective measure to take to display a vibration stimulus to the skin surface.
A number of researches that are based on such an idea have been reported so far. For example, Japanese Patent Application Laid-Open Publication No. 11-150794 discloses, in particular, on pp. 3-5 and FIG. 1, a tactile display method for displaying a tactile sensation by using a huge number of microactuators with electromagnetic coil. Those microactuators are arranged at very narrow intervals of about 2 mm and are pressed against a person's palm. They confirmed via experiments that by supplying appropriately controlled amounts of drive current in mutually different phases to those actuators, the person would get multiple different kinds of tactile sensations at his or her palm to which those actuators are pressed.
Likewise, Konyo, Tadokoro, Takamori, Oguro and Tokuda, “Tactile Feeling Display for Touch of Cloth Using Soft High Polymer Gel Actuators”, TVRSJ, Vol. 6, No. 4 (2001), pp. 323-328 (hereinafter referred to as “Konyo et al.”) discloses a similar method for displaying a vibration stimulus to a person's finger pulp surface by arranging two-dimensionally fibers of ion conductive polymer gel called “ICP actuators” and applying an oscillatory voltage to those fibers. According to their technique, the oscillatory voltage to apply is a combined wave of two signals with mutually different frequencies. And they also confirmed via psychological experiments that by changing the combinations of the frequencies, the subject got tactile sensations as if he or she felt a number of different pieces of cloth.
In these examples, they just defined experimentally how a person's tactile sensation would change with a drive signal applied to a tactile simulator. However, various inventions have already been made as to how to synthesize a tactile simulation signal for simulating a particular tactile sensation. For example, Japanese Patent Application Laid-Open Publication No. 9-155785 (hereinafter referred to as “JP9-155785”) discloses, in particular, on pp. 3-4 and FIG. 1, a method for displaying an object's feel by synthesizing a tactile simulation signal based on a sensor signal, which has been obtained through a direct contact with the object, and by reference to a table. In that table, stored are various parameters that are essential to the tactile sensation to simulate and that determine the tactile simulation signal. Examples of those parameters include waveform period, amplitude, and rise and fall times. The tactile simulation signal is synthesized based on these parameters.
On the other hand, Japanese Patent Application Laid-Open Publication No. 2001-306200 (hereinafter referred to as “JP2001-306200”) discloses, in particular, on p. 6 and FIG. 10, a method for defining a number of different tactile simulation signals in advance as basic simulation signals. This method is based on the fact that two objects with similar surface shapes would produce reactive forces with similar oscillating waveforms when touched. In generating a tactile simulation signal for a given object, it is determined which basic simulation signal needs to be used and then the waveform of the basic simulation signal is shaped according to a difference in surface shape of the object from others.
Furthermore, Japanese Patent Application Laid-Open Publication No. 2006-58973 (hereinafter referred to as “JP2006-58973”) discloses, in particular, on pp. 9-11 and FIG. 11, a method for generating a tactile simulation signal by extracting and breaking down waves with typical frequencies and amplitudes from an oscillating waveform representing the force that has been obtained with a sensor and by shaping and synthesizing together those waves according to the property of the person's tactile sensation.
According to these conventional technologies, however, the tactile sensations of only limited kinds of objects can be simulated. In addition, just limited types of tactile sensations can barely be simulated and far from being natural.
Generally speaking, a tactile simulation signal is synthesized by performing roughly two processing steps of: sensing an object, of which the tactile sensation needs to be simulated, to obtain material information (Step 1); and synthesizing a tactile simulation signal based on a result of that sensing (Step 2). FIG. 1 illustrates a specific example of these two processing steps 1 and 2 for synthesizing a tactile simulation signal. In Step 2, the feedback signal is synthesized based on only the information that has been collected in advance and the information that has been obtained in Step 1 about the object, of which the tactile sensation needs to be simulated. That is why according to such a method, if any other piece of information is required, the tactile sensation of the object cannot be simulated.
According to JP9-155785, for example, to synthesize a tactile simulation signal, a table that stores parameters determining the tactile simulation signal is made reference to. With such a method adopted, if no item on the table applies to a result obtained by the object sensing processing step 1, the tactile simulation signal cannot be synthesized.
The same can be said about JP2001-306200, in which tactile simulation signals are defined in advance as basic simulation signals and in which the tactile simulation signal of an object cannot be synthesized, either, unless the object falls within the range of those basic simulation signals. As a result, only the tactile sensations of prepared objects can be simulated. That is to say, the range of objects, of which the tactile sensations can be simulated, is very narrow.
As far as the synthesis of the tactile simulation signal is concerned, there are various sorts of approaches, which can be classified into the two major categories. One approach is pre-designing models for synthesizing the tactile simulation signal based on either physical data or the data about persons' tactile sensation properties and setting parameters using the information that has been obtained about the object in the processing step 1, thereby synthesizing the signal. The other approach is generating the tactile simulation signal by shaping a time waveform signal that has been obtained by a sensor.
The former approach is taken by JP9-155785, for example. According to JP9-155785, to display a tactile sensation as a vibration of a voice coil motor, the parameters of that vibration, including the oscillation period, amplitude, and rise and fall times, are determined based on a result obtained by sensing the object. However, no model that can perfectly describe, for every possible combination of materials, what kind of frictional vibration will be produced when the two materials rub against each other has ever been discovered. Likewise, sufficient knowledge has not been obtained yet as to what combination of firing patterns of the tactile receptors or what kind of vibration of the skin surface makes the person get a soft feel or a rough feel, for example.
Under the circumstances such as these, it is unthinkable that each and every one of tactile sensations that a person would get by feeling various materials can be simulated with such a tactile simulation signal that has been synthesized based on a simple model. According to JP9-155785, among other things, the oscillation frequency of the actuator is a single frequency, and therefore, the number of tactile sensations that can be simulated should be very small.
On the other hand, according to the latter approach of shaping the waveform of a signal obtained from a sensor, it is very important how much the vibration stimulus that a tactile simulator displays to the person's skin surface resembles the frictional vibration to be produced when the skin actually rubs the object. In this case, there are two pairs of materials to rub against each other. Even though one of the two materials is the same in the two pairs, the other material of one pair is different from that of the other. That is why the frictional vibration produced by one pair should be different from the one produced by the other. That is to say, the vibration produced by rubbing the object with the sensor should be different from the one produced by rubbing the same object with the skin. For that reason, if the latter approach is taken, the signal waveform needs to be shaped with such a variation in oscillating waveform taken into account. According to JP2006-58973, a time waveform signal is obtained using force detecting sensors or acceleration sensors that are attached to the fingertips of a glove and then has its waveform shaped adaptively to the human tactile sensation property. Nevertheless, JP2006-58973 does not pay attention to the fact that the vibration property of the glove is different from that of the finger elastic body. In that sense, even if the technique disclosed in JP2006-58973 is adopted, the person should not be able to get a realistic tactile sensation for the reasons described above.